This application is in response to RFA HL-02-001 entitled Transfusion Medicine/Hemostasis Clinical Network and is a consortium of the New York Presbyterian Hospital - Weill Cornell College of Medicine-Columbia College of Physicians and Surgeons. It provides health care to > 20% of the New York City metropolitan area and has access to > 20 million people within 2 hours. It is an amalgam of physicians and scientists involved in clinical research in Hemostasis and Transfusion Medicine with expertise in Pediatrics, Internal Medicine, Pathology, and Surgery. The group has both the patient population and the clinical expertise required to participate in clinical trials proposed by other centers in the Network. Specific Aim 1 is a clinical trial of refractory ITP, defined as children and adults with ITP who have failed to respond to splenectomy. It intends to focus on the pathophysiology of refractory ITP by comparing two novel treatments. One, rituximab, is an anti-CD20 which depletes the recipient of B cells and should be an effective immunosuppressant in a "pure" autoantibody disease like ITP. There is preliminary data describing its effectiveness which should optimize its use. The other arm intends to use thrombopoietin or mimetic (TPO) to increase the platelet count by stimulating platelet production. This arm hypothesizes that a critical element in refractory ITP is a decreased production of platelets which can be rectified by stimulation with TPO. A registry of splenectomy will be included to facilitate enrollment of eligible patients. Specific Aim 2 intends to optimize granulocytes for transfusion. This would be of great potential benefit to patients with prolonged, severe neutropenia who suffer considerable morbidity and occasional mortality from infection. There is also the high cost of prolonged hospitalizations. In the past, studies of granulocyte transfusion showed little benefit and significant toxicity. The current study will explore different methods of preparation of granulocytes and also novel techniques for evaluation of their efficacy. Specific Aim 3 demonstrates that the consortium is able to participate in protocols for a wide variety of disorders of hemostasis and transfusion medicine. The consortium includes Dr. Grima of the NY Blood Center who annually phereses approximately 20 TTP patients; a leading center, Cornell, for management of patients with alloimmune thrombocytopenia;and a large hemophilia center.